The present invention relates generally to a dynamic behavior control apparatus for an automotive vehicle, and more specifically, to a method and apparatus for controlling the roll characteristics of the vehicle by controlling the rear steering direction and brakes of the vehicle.
Dynamic control systems for automotive vehicles have recently begun to be offered on various products. Dynamic control systems typically control the yaw of the vehicle by controlling the braking effort at the various wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based upon the steering wheel angle and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained. Typically, the dynamic control systems do not address roll of the vehicle. For high profile vehicles in particular, it would be desirable to control the roll over characteristic of the vehicle to maintain the vehicle position with respect to the road. That is, it is desirable to maintain contact of each of the four tires of the vehicle on the road.
Vehicle rollover and tilt control (or body roll) are distinguishable dynamic characteristics. Tilt control maintains the vehicle body on a plane or nearly on a plane parallel to the road surface. Roll over control is maintaining the vehicle wheels on the road surface. One system of tilt control is described in U.S. Pat. No. 5,869,943. The ""943 patent uses the combination of yaw control and tilt control to maintain the vehicle body horizontal while turning. The system is used in conjunction with the front outside wheels only. To control tilt, a brake force is applied to the front outside wheels of a turn.
One known yaw control system described in U.S. Pat. No. 5,634,698 uses rear wheel steering to help achieve yaw stability using brake control. However, this system does not provide or teach the use of such a control for preventing rollover of the vehicle.
Another known system for preventing rollover is found in U.S. Pat. No. 6,065,558, which applies brakes to the outside front wheels to prevent rollover. In certain maneuvers, however, application of front brakes alone may not be desirable due to the particular handling characteristics of the vehicle.
It would therefore be desirable to provide a roll stability system that detects a potential rollover condition and temporarily applies steering and braking in a desired direction to counter rollover.
It is therefore an object of the invention to provide a roll control system for use in a vehicle using steering direction of the rear wheels together with application of brakes.
In one aspect of the invention, stability control system for an automotive vehicle includes a plurality of sensors sensing the dynamic conditions of the vehicle and a controller that controls a rear steering direction and brake force to reduce a tire moment so the net moment of the vehicle is counter to the roll direction. The sensors may include a speed sensor, a lateral acceleration sensor, a longitudinal acceleration sensor, a roll rate sensor, and a yaw rate sensor. A controller is coupled to the sensors to determine a roll angle estimate. The controller determines the direction and steering effort change in response to the relative roll angle estimate to counter roll.
In a further aspect of the invention, a method of controlling roll stability of the vehicle comprises the steps of:
determining a roll angle estimate in response to a rollover sensor; and
controlling a rear steering actuator and a brake controller to a predetermined tire force vector in response to the relative roll angle estimate.
One advantage of the invention is that such systems may be easily implemented into a steer-by-wire system.